The capacity of the crane, i.e. its ability to lift a load, is based, in part, on its stability. Stability, in turn, is related to the gage or spacing between the tread members. A wide gage will improve stability and hence generally incrase capacity. However, a wide gage can restrict the mobility of the crane on certain job sites. The virtues of both wide gage (improve stability) and narrow gage (improve mobility) have been satisfactorily attained by prior art arrangements permitting adjustment of axle length. However, such arrangements are expensive and some applications of cranes do not require such capability. For those applications, a fixed length axle is acceptable and has been widely utilized. Thus, the same crane model often must be produced in two versions; one with adjustable axle length and one with fixed axle length. This requirement has necessitated different car bodies and tread members in addition to different axles for the same model crane. As a consequent, certain economies of scale are lost and the cost of manufacturing both versions of the same model of crane is high.
The present invention provides a construction in which the fixed and adjustable length axles may be readily utilized with a common car body and common tread members, so that the desired economies of scale can be attained with respect to the use of those components. The invention also provides a construction for the axles which permits a single axle of each type to be used for both front and rear axles. The attachment of both fixed and adjustable length axles to the car body and tread members is achieved with simple pin connections to simplify not only initial assembly, but also disassemble for transport of the crane components from one job site to another and subsequent reassemble.